Journal
JOURNAL OF IMMUNOLOGY
Volume 194, Issue 9, Pages 4507-4517Publisher
AMER ASSOC IMMUNOLOGISTS
DOI: 10.4049/jimmunol.1402321
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Funding
- Sao Paulo Research Foundation [2012/14524-9, 2013/08216-2, 2013/21295-9]
- University of Sao Paulo Nucleo de Apoio a Pesquisa em Doencas Inflamatorias Grant [11.1.21625.01.0]
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Pathogens are sensed by innate immune receptors that initiate an efficient adaptive immune response upon activation. The elements of the innate immune recognition process for Paracoccidioides brasiliensis include TLR-2, TLR-4, and dectin-1. However, there are additional receptors necessary for the host immune responses to P. brasiliensis. The nucleotide-binding oligomerization domain-like receptor (NLRs), which activate inflammasomes, are candidate receptors that deserve renewed investigation. After pathogen infection, the NLRs form large signaling platforms called inflammasomes, which lead to caspase-1 activation and maturation of proinflammatory cytokines (IL-18 and IL-1 beta). In this study, we showed that NLR family pyrin domain-containing 3 (Nlrp3) is required to induce caspase-1 activation and further secretion of IL-1 beta and IL-18 by P. brasiliensis-infected macrophages. Additionally, potassium efflux and lysosomal acidification induced by the fungus were important steps in the caspase-1 activation mechanism. Notably, Nlrp3 and caspase-1 knockout mice were more susceptible to infection than were the wild-type animals, suggesting that the Nlrp3-dependent inflammasomes contribute to host protection against P. brasiliensis. This protective effect occurred owing to the inflammatory response mediated by IL-18, as shown by an augmented fungus burden in IL-18 knockout mice. Taken together, our results show that the Nlrp3 inflammasome is essential for resistance against P. brasiliensis because it orchestrates robust caspase-1 activation and triggers an IL-18-dependent proinflammatory response.
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